We have performed left lung transplantations in 15 dogs for one year and six months from June, 1990 to December, 1991 at the Repartment of Thoracic and Cardiovascular Surgery Yonsei University College of medicine, Seoul, Korea. These dogs were sacrificed at from operative day to post-operative 15 days when their general conditions were deteriorated. The gross findings of the transplanted lungs were thrombi in left atrium in three cases, partial occlusion of pulmonary artery or pulmonary veins in three cases, hemorrhage at pulmonary arterial anastomotic site in one case and bronchial anastomotic stenosis in two cases, bronchial anastomotic rupture in one case % no abnormal gross findings in four cases. The microscopic findings of the transplanted lungs were hemorrhagic infarction in one case, perivascular hemorrhage or pulmonary edema in two cases, peribronchial inflammatory cell infiltration & pneumonia in three cases, and alveolar type rejection with infiltration of type II pneumocytes and septal thickening in 3 cases. And also there were no abnormal findings including rejection or inflammatory evidences in six cases. The one among these six dogs survived to 15 days without evidence of rejection or inflammatory reaction & died due to postoperative care accident.